The subject matter disclosed herein relates to the art of turbomachines and, more particularly, to a method and apparatus for repairing a gas turbine rotor wheel.
In general, turbomachines include a number of stages each having an associated rotor wheel. The rotor wheel includes an outer circumferential surface that supports a plurality of buckets or blades. The blades are secured to the rotor wheel through a dove tail interface provided on the outer circumferential surface. The dovetail interface includes a plurality of acute corners that define a dove tail slot that extends axially along the circumferential surface. Each bucket includes a base portion having a mating dovetail member. During operation, the rotor wheel rotates at very high speeds and is subjected to high thermal gradients. The high speeds and thermal gradients create stresses at the acute corners of the dovetail interface. Over time, cracks develop near the acute corners as a result of the stresses.
Conventional methods for repairing a rotor disk require removal of the blades and allow repair of cracks having a length of less than 0.25 inches (6.35 mm). In cases where the crack is greater than 0.25 inches, no repair option is presently available. As such, in the event a crack of greater than 0.25 inches is found, the rotor wheel must be scrapped. Scrapping a rotor wheel leads to a direct increase in operational cost of the turbomachine due to down time and service time required to dissemble the associated turbine stage, remove the rotor wheel, dissemble the blades, install the blades on a new rotor wheel and subsequently install the new rotor wheel in the turbomachine.